What is a canonical data model?

Recently, I have been asked a lot "What is a canonical data model?". In the SOA world, the term "canonical data model" is thrown around as a way to impress the lay person. In reality the canonical data model is a simple concept:

The canonical data model (CDM) is a representation of common information produced and consumed by applications. The CDM is normally used to publish events in the form of messages out of one application into several another applications. The CDM is used as the format of the message so that all of the receiving applications know what information to expect in the message.

For example lets create the canonical data model for a person. The CDM for a person must include information that uniquely identifies that person:

• Name
• Birth Date
• Social Security Number/Passport number

The information that is unique must be included in the CDM so that it is easy to distinguish if two person messages relate to the same person or different people. That is the lowest common denominator for a canonical message. A canonical message normally contains other useful information about an object that is used by most of the receiving applications. Continuing to build out the CDM for our person object, these other useful fields could be included:

• Work Address
• Home Address
• Work phone number
• Home phone number
• Cell phone number
• Fax number

As you can see the list of information describing a person can go on and on. The information each application needs to know about a person can vary greatly, so how do you know what to put in the canonical data model? In my next post, I will talk about how to create a canonical data model that provides the benefits without running into a maintenance nightmare.